The Serbian National Assembly building in Belgrade

This combo of pictures shows the Serbian National Assembly building with the lights on (top) and with the lights off (bottom) during the annual Earth Hour event in Belgrade on March 31, 2012.

This combo of pictures shows the Serbian National Assembly building with the lights on (top) and with the lights off (bottom) during the annual Earth Hour event in Belgrade on March 31, 2012. (ANDREJ ISAKOVIC/AFP)

This combo of pictures shows the Serbian National Assembly building with the lights on (top) and with the lights off (bottom) during the annual Earth Hour event in Belgrade on March 31, 2012.